Chum et al [1]} proposed the following query expansion approach. For query \(q\) , a new query sample can be formed by taking average over top-\(n\)  spatially verified samples \(\mathcal {F}\)  from ranked list \(L(q)\) ,
\(q_{\text{avg}} = \frac{1}{|\mathcal {F}|+1} \left(q + \sum _{f \ in \mathcal {F}} f \right)\) 
